How to prevent bypassing Screen Time passcode using Face ID on iPhone?

Ask someone else to enter their Apple Account/Password for the reset method after they set the Passcode for you. That way they will be required to enter their credentials to reset the password and you will not be able to make any changes to the limits or restrictions unless you Factory Reset the device where all data will be lost.

As the owner of the device, you will always have a way to turn off Screen Time, otherwise users would end up with a bricked devices, simply because they forgot their Passcode. Apple does not know what it is, so you cannot ask them. Would you prefer to buy a new device if you forgot your Screen Time Passcode?

The purpose is for adding Parental Controls to a child's device that they cannot disable. Screen Time alone without any Passcode gives the owner of the device the information to monitor their activities themselves and of course how they use that information is entirely up to them.

SravanKrA wrote:

How to reset Screen Time Passcode

From how I read the post, the OP has no problem resetting the Passcode and the issue is that they know the Passcode they enter and can reset it themselves easily when they enter their Apple Account/Password that has been added as a reset option. It seems they want to lock the Screen Time settings so they are unable to change it, and that is why I recommended to have someones else enter the Passcode and they can use their own Apple Account/Password for the reset method and the OP won't know what it is.

This is not the same as signing someone else's Apple Account into the device where that may result in it being bricked where the OP will no longer be able to use it without an Activation Lock removal request, since the reset of the Screen Time Passcode is still possible, it just may result in data loss.

SravanKrA wrote:

Mac Jim ID wrote:

Ask someone else

This phrase is somewhat unclear. I presume you meant the Parent/Guardian.

No, it could be a friend or anyone else that you want to trust with the responsibility of keeping the Screen Time Passcode from the OP that does not have the self control to keep the limits set with their own Screen Time Passcode. That way the consequences of the owner resetting the Passcode with a Factory Reset are more significant, since the iCloud backup cannot be used and results in data loss for anything not stored in iCloud.

How to reset Screen Time Passcode

If you are unable to reset your Screen Time Passcode with your Apple ID then you may have skipped the option while setting up Screen time Passcode. See the pic below

If you have forgotten your Screen Time passcode. There are two options.

If you are unable to reset the Screen Time passcode from this-> link, then you will need a computer for option 2. If you don't have one, borrow one from a friend.

Option 1

Use this link to reset your passcode --> If you forgot your Screen Time passcode - Apple Support

Option 2

Forgot? Click below to reset…

Click->If you forgot the passcode for your iPhone, iPad, or iPod touch, or your ...

If you have chosen option 2, then regarding your data, if…

1. You have an iCloud or iTunes backup. I am sorry, there is no use of a backup because if you restore from your backup, your Screen Time Passcode will be back. 
2. You have synced your data to iCloud, then what you will get back is what you have synced to iCloud and uploaded to iCloud Drive; the information that is synced and stored in iCloud are, Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos, shared photos, iCloud Photos*, Health data, call history, and files you store in iCloud Drive. (*-If you had turned on iCloud Photos, your content is automatically stored in iCloud.)
3. You have imported your Photos & Videos to Mac/PC, then they are safely residing there
4. You have uploaded some of it to Cloud Drives using the Files app (iCloud Drive, Google Drive, OneDrive, Dropbox, Flickr, box, AmazonDrive, Adobe Creative Cloud, etc.)
5. If you have not imported, nor have you synced or uploaded your data to cloud drives, before forgetting the Screen Time passcode, then I am sorry, all your data is lost.

Mac Jim ID wrote:

Ask someone else

This phrase is somewhat unclear. I presume you meant the Parent/Guardian.